1. Field of the Invention
This invention relates to a magnetic recording medium adapted for an encoder used to detect an angle, a rotating speed or a position.
2. Description of the Prior Art
Heretofore, a conventional magnetic recording medium used for a magnetic encoder has been made of a plastic magnet.
However, the magnetic recording density of the magnetic recording medium made of the plastic magnet cannot be enhanced, and such magnetic recording medium does not satisfy the accuracy requirements of the encoder.
In order to eliminate the drawbacks, there is proposed a magnetic recording medium made of iron-cobalt-chromium alloy magnet adapted for a vertical magnetic recording system.
However, since the magnetic recording medium made of this alloy magnet must be heat treated in a strong magnetic field at the time of fabrication, its manufacturing cost is high.
A sputtered film of a cobalt alloy or an electroless plating film is proposed as a vertical recording medium, but both have low coercive force, and cannot be used for a magnetic encoder.
Further, as shown in FIG. 3, it is also difficult to form a medium on the circumferential portion of a drum.